Types of Deep Drawn Parts: Simple, Average & Difficult Geometries

How Deep-Drawn Part Difficulty Is Classified

Not every “deep drawn part” is equally hard to make. Shops grade difficulty on a spectrum because the difference between an easy cup and a deep, thin-walled housing changes the tooling, the number of press strokes, the scrap rate, and the price you are quoted. The practical split used across the industry is three buckets: simple, average, and difficult geometries.

The single number that decides the bucket is the limiting draw ratio (LDR). It compares the blank diameter to the punch diameter. A high LDR means the part draws easily in one or two strokes; a low LDR means the metal would tear if you tried to form it in one hit, so you need several redraws. From there, wall-thickness variation, aspect ratio, material, and tolerance tighten or loosen the difficulty.

Simple Deep Drawn Parts

Simple parts sit at LDR above roughly 2.0. They form in one or two draws, hold generous corner radii, and tolerate standard commercial tolerances. Think of the classic cylindrical cup: a flat blank becomes a open shell in a single stroke with little wall thinning.

Typical simple parts include:

• Caps, lids, and closures
• Basic cylindrical sensor housings
• Plain sleeves and bushings
• Shallow trays and cans

Because tooling is short and yields are high, simple parts are the cheapest to produce at volume and the easiest to source. If your design can stay in this bucket, do it — most cost savings in deep drawing come from avoiding the next two tiers.

Average-Difficulty Parts

Average parts land around LDR 1.6 to 2.0. They need three or four draws with intermediate anneals, tighter radii, and more careful blank control. Wall thinning becomes a real design constraint rather than an afterthought.

Common average parts:

• Battery cans and cell cases
• Connector shells with steps or flanges
• Medium aspect-ratio tubes and sleeves
• Housings with a formed bottom feature

These are the bread-and-butter of a competent deep drawn parts supplier. The tooling cost is moderate and lead times are predictable once the draw schedule is validated. Read our Deep Drawing: Process, Materials & Design Guide for the full step sequence.

Difficult Geometries

Difficult parts sit below LDR 1.6 and often combine several hostile features at once: deep draw depth, thin walls, non-round cross-sections, stepped diameters, or sealed designs that hide the draw seam. They may need five or more draws, in-process annealing, and tight process control to hold dimensions.

Examples that fall here:

• Deep, narrow tubes with high aspect ratio
• Stepped or tapered cups
• Square, rectangular, or oval drawn shells
• Sealed deep drawn covers with hidden seams
• Aerospace and medical housings with fine tolerances

Difficult parts are where supplier skill shows. A shop that only runs simple cups will push you to redesign; one with in-house tooling and process engineering will hold the geometry. Our Deep Drawn Covers design and sourcing guide walks through the sealed-cover case in detail.

What Actually Drives the Difficulty

Beyond the draw ratio, five factors move a part up the difficulty ladder:

• Material. Stainless steel work-hardens fast and springs back; aluminium draws easily but dents. The alloy sets your redraw count.
• Aspect ratio. Deeper and narrower means more draws and more wall-thinning risk.
• Wall thinning. Thin walls near the punch radius tear first, forcing slower, multi-stage draws.
• Corner radii. Sharp corners need more force and crack sooner than generous radii.
• Tolerance. Tight diameters or flatness demand extra forming and inspection steps.

Designing for an Easier Draw

You rarely need the hardest possible geometry. A few design-for-manufacture moves keep a part in the simple or average bucket:

• Open up corner radii wherever function allows.
• Avoid wall thickness below about 0.3 mm on deep parts.
• Keep aspect ratio under 3:1 before accepting extra draws.
• Specify stainless steel only where corrosion or strength demands it.
• Confirm the draw ratio early with a blank-diameter calculator.

See the advantages of deep drawn manufacturing to understand why the process beats machining or welding on cost and strength for these shapes.

How the Difficulty Tier Changes Your Quote

The tier your part falls into does not just change the engineering — it changes the commercial terms you get back. Because tooling, press time and yield all move together, a part that slips from the simple bucket into the average bucket can cost meaningfully more per piece even though the drawing barely changed.

Simple parts quote fast and cheap because the die is short, the draw schedule is one or two stations, and scrap stays low. Average parts add redraws, intermediate annealing and a longer try-out, so both the tooling figure and the per-piece price rise. Difficult parts carry the longest lead time of all: more stations, more process control, more inspection, and usually a sampling round before the line is released for production.

That is why the cheapest saving available to a buyer is usually a small design change that keeps a part one tier lower. Opening a corner radius, trimming draw depth, or relaxing a diameter tolerance can move a part back down a tier and cut both tooling and piece price at once.

Parts We Draw at Each Tier

Three real examples show how the tiers look on the shop floor.

• Simple. A shallow round shell with generous radii, drawn in one hit and trimmed to length. Our steel deep drawn ring cup with notched rim is typical — short tool, high yield, fast to quote.
• Average. A box or tray with straight walls and a flange needs several draws and closer blank control. The steel deep drawn cubic box with dual side holes sits in this band: formable, but no longer a one-stroke part.
• Difficult. Deep, narrow or stepped geometry with thin walls. The steel deep drawn long tube with expanded sections is the kind of profile that needs a full draw schedule, annealing between stages and tight process control to hold the expanded diameters.

Choosing a Tier Before You Send the Drawing

Before you request a quote, run the part through three checks: the blank-to-punch ratio, the aspect ratio, and the tolerance you actually need on each surface. If the ratio is comfortable and only one or two dimensions are critical, say so on the drawing — that lets the supplier quote the easy version of your part instead of the worst case.

For the draw-ratio maths behind those checks, use our limiting draw ratio reference; for the cost side of the same decision, see how deep drawn parts reduce manufacturing costs.

Common Misconceptions About Part Difficulty

Three beliefs come up repeatedly in enquiries, and all three usually cost the buyer money.

• “Deeper is always harder.” Not necessarily. A deep part with generous radii and thick walls can draw more easily than a shallow part with sharp corners and a tight tolerance. Depth matters only relative to diameter and wall thickness.
• “Stainless steel is always the difficult option.” Stainless steel work-hardens, but a well-designed austenitic part with sensible radii runs predictably. Poor geometry in an easy alloy is the more common cause of trouble.
• “Non-round shapes cannot be drawn.” Square, rectangular and oval shells are drawn routinely; they simply need more blank control and more attention to corner radii than a round shell.

What actually decides difficulty is the combination — ratio, radii, wall, material and tolerance read together — which is why two parts that look similar on a drawing can sit in different tiers once the draw schedule is worked out.

Prototyping Before You Commit to Tooling

For difficult geometries, a prototype stage is usually cheaper than a redesign after the tool is cut. Soft tooling or a single-station die can produce a handful of parts that confirm the draw schedule, the wall thinning and the final dimensions before you pay for the production tool.

That sample also settles questions a drawing cannot: whether the part releases from the punch, whether the trim edge is acceptable, and whether the surface survives handling. Send those findings back into the drawing, and the production quote usually comes back lower than the first estimate.

Frequently Asked Questions

What is a simple deep drawn part?

A simple deep drawn part forms in one or two draws at a limiting draw ratio above about 2.0, with generous radii and standard tolerances — cups, caps, cans, and basic sleeves are typical.

When is a deep drawn part considered difficult?

A part is difficult when its limiting draw ratio falls below about 1.6, or when it combines deep draw depth, thin walls, non-round sections, sealed seams, or fine tolerances that require five or more draws and tight process control.

Does stainless steel make a part harder to draw?

Yes. Stainless steel work-hardens quickly and has high springback, so it usually needs more redraws and annealing than aluminium or mild steel. That raises tooling complexity but delivers the corrosion resistance many parts require.

How do I know which bucket my part is in?

Start from the blank-to-punch diameter ratio and the aspect ratio, then check material and tolerance. A limiting draw ratio reference and blank-diameter calculator will place the part in the simple, average, or difficult range.